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Types of Biodiversity
Traditionally, ecologists have measured biodiversity, a general term for the variety present in the biosphere, by taking into account both the number of species and their commonness.
Biodiversity can be estimated at a number of levels of organization of living things. These estimation indexes, are most useful as a first step in quantifying biodiversity within ecosystems. However, biologists recognize that measures of biodiversity, in terms of species diversity, may help focus efforts to preserve the biologically or technologically important elements of biodiversity.
In the 1980s, biologists working in Lake Victoria in Africa discovered one of the most extraordinary products of evolution on the planet. Located in the Great Rift Valley, Lake Victoria is a large lake about 68,900 km in area (larger than Lake Huron, the second largest of North America’s Great Lakes).
Biologists were studying species of a family of fish called cichlids. They found that as they sampled for fish in different locations of the lake, they never stopped finding new species, and they identified nearly 500 evolved types of cichlids.
But while studying these variations, they quickly discovered that the invasive Nile Perch was destroying the lake’s cichlid population, bringing hundreds of cichlid species to extinction with devastating rapidity.
The Lake Victoria cichlids provide an example through which we can begin to understand biodiversity.
The biologists studying cichlids in the 1980s discovered hundreds of cichlid species representing a variety of specializations to particular habitat types and specific feeding strategies: eating plankton floating in the water, scraping and then eating algae from rocks, eating insect larvae from the bottom, and eating the eggs of other species of cichlid.
The cichlids of Lake Victoria are the product of an adaptive radiation.
An adaptive radiation is a rapid (less than three million years in the case of the Lake Victoria cichlids) branching through speciation of a phylogenetic tree into many closely related species; typically, the species “radiate” into different habitats and niches. The Galapagos finches are an example of a modest adaptive radiation with 15 species. The cichlids of Lake Victoria are an example of a spectacular adaptive radiation that includes about 500 species.
At the time biologists were making this discovery, some species began to quickly disappear.
The Nile perch was introduced in 1963, but in the 1980s its populations began to surge. The Nile perch population grew by consuming cichlids, driving species after species to the point of extinction (the disappearance of a species). In fact, there were other factors that played a role in the extinction of perhaps 200 cichlid species in Lake Victoria, such as, the Nile perch, declining lake water quality due to agriculture and land clearing on the shore, and increased fishing pressure.
The cichlids of Lake Victoria are a thumbnail sketch of contemporary rapid species loss that occurs all over Earth and is caused by human activity.
Extinction is a natural process of macroevolution that occurs at the rate of about one out of 1 million species becoming extinct per year. The fossil record reveals that there have been five periods of mass extinction in history with much higher rates of species loss, and the rate of species loss today is comparable to those periods.
There is a major difference between the previous mass extinctions and the current extinction we are experiencing: human activity. Specifically, three human activities have a major impact:
Destruction of habitat
Introduction of exotic species
Predictions of species loss within the next century, a tiny amount of time on geological timescales, range from 10 percent to 50 percent.
Extinctions on this scale have only happened five other times in the history of the planet, and they have been caused by cataclysmic events that changed the course of the history of life in each instance. Earth is now in one of those times.
Genetic diversity or variation is the raw material for adaptation in a species. A species’ future potential for adaptation depends on the genetic diversity held in the genomes of the individuals that make up the species.
The same is true for higher taxonomic categories. A genus with very different types of species will have more genetic diversity than a genus with species that look alike and have similar ecologies.
Many genes code for proteins, which in turn carry out the metabolic processes that keep organisms alive and reproducing.
Genetic diversity can be measured as chemical diversity in that different species produce a variety of chemicals in their cells, both the proteins as well as the products and byproducts of metabolism. This chemical diversity has potential benefit for humans as a source of pharmaceuticals, so it provides one way to measure diversity that is important to human health and welfare.
Humans have generated diversity in domestic animals, plants, and fungi.
This diversity is also suffering losses because of migration, market forces, and increasing globalism in agriculture, especially in heavily populated regions such as China, India, and Japan.
The human population directly depends on this diversity as a stable food source, and its decline is troubling biologists and agricultural scientists.
Ecosystem diversity, is defined as the number of different ecosystems on the planet or in a given geographic area.
Whole ecosystems can disappear even if some of the species might survive by adapting to other ecosystems. The loss of an ecosystem means the loss of interactions between species, the loss of unique features of coadaptation, and the loss of biological productivity that an ecosystem is able to create. An example of a largely extinct ecosystem in North America is the prairie ecosystem. Prairies once spanned central North America from the boreal forest in northern Canada down into Mexico.
The Prairies that once spanned central North
America are now all but gone, replaced by
crop fields, pasture lands, and suburban
Many of the species survive, but the hugely
productive ecosystem that was responsible
for creating the most productive agricultural
soils is now gone.
As a consequence, soils are disappearing or must be maintained at greater expense.
Despite considerable effort, knowledge of the species that inhabit the planet is limited.
A recent estimate suggests that the eukaryote species (any organism whose cells contain a nucleus and other organelles enclosed within membranes), for which science has named about 1.5 million species, account for less than 20 percent of the total number of eukaryote species present on the planet (8.7 million species, by one estimate).
Estimates of numbers of prokaryotic species (a single-celled organism that lacks a membrane bound nucleus) are largely guesses, but biologists agree that science has only begun to catalog their diversity.
Even with what is known, there is no central repository of names or samples of the described species; therefore, there is no way to be sure that the 1.5 million descriptions is an accurate number.
Naming and counting species may seem an unimportant pursuit given the other needs of humanity, but it is not simply an accounting. Describing species is a complex process by which biologists determine an organism’s unique characteristics.
The unique characteristics of each species make it potentially valuable to humans or other species on which humans depend. Understanding these characteristics is the value of finding and naming species.
Biodiversity is not evenly distributed on Earth. Lake Victoria contained almost 500 endemic species of cichlids, as these species were found only in Lake Victoria, ignoring the other fish families present in the lake.
Endemic species are found in only one location. Endemics with highly restricted distributions are particularly vulnerable to extinction.
Lake Victoria contains hundreds of species of fish while Lake Huron in the US, contains about 79 species of fish, all of which are found in many other lakes in North America. What accounts for the difference in fish diversity in these two lakes?
Lake Victoria is a tropical lake, while Lake Huron is a temperate lake. Lake Huron in its present form is only about 7,000 years old, while Lake Victoria in its present form is about 15,000 years old.
Biogeographers have suggested these two factors, latitude and age, are two of several hypotheses to explain biodiversity patterns on the planet.
One of the oldest observed patterns in ecology is that species biodiversity in almost every taxonomic group increases as latitude declines. In other words, biodiversity increases closer to the equator.
It is not yet clear why but hypotheses include the greater age of the ecosystems in the tropics versus temperate regions that were largely devoid of life or drastically impoverished during the last glaciation. The idea is that greater age provides more time for speciation. Another possible explanation is the increased energy the tropics receive from the sun versus the decreased energy that temperate and polar regions receive.
The complexity of tropical ecosystems may promote speciation by increasing the heterogeneity, or number of ecological niches, in the tropics relative to higher latitudes.
The greater heterogeneity provides more opportunities for co-evolution, specialization, and perhaps greater selection pressures leading to population differentiation.
However, this hypothesis suffers from some circularity-ecosystems with more species encourage speciation, but how did they get more species to begin with? The tropics have been perceived as being more stable than temperate regions, which have a pronounced climate and day-length seasonality. The tropics have their own forms of seasonality, such as rainfall but they are generally assumed to be more stable environments and this stability might promote speciation.
The rate of endemism is highest, and there are more biodiversity hotspots. However, this richness of diversity also means that knowledge of species is lowest, and there is a high potential for biodiversity loss.
In 1988, British environmentalist Norman Myers developed a conservation concept to identify areas rich in species and at significant risk for species loss: biodiversity hotspots.
Biodiversity hotspots are geographical areas that contain high numbers of endemic species. The purpose was to identify important locations on the planet for conservation efforts. By protecting hotspots, governments can protect a larger number of species.
The original criteria for a hotspot included the presence of 1500 or more endemic plant species and 70 percent of the area disturbed by human activity. There are now 34 biodiversity hotspots containing large numbers of endemic species, including animals and plant species. The thirty four biodiversity hotspots, cover only 2.3 percent of the Earth’s surface but have endemic to them 42 percent of the terrestrial vertebrate species and 50 percent of the world’s plants.
adaptive radiation rapid branching through speciation of a phylogenetic tree into many closely related species
biodiversity hotspot concept originated by Norman Myers to describe a geographical region with a large number of endemic species and a large percentage of degraded habitat
biodiversity variety of a biological system, typically conceived as the number of species, but also applying to genes, biochemistry, and ecosystems
bush meat wild-caught animal used as food (typically mammals, birds, and reptiles); usually referring to hunting in the tropics of sub-Saharan Africa, Asia, and the Americas
chemical diversity variety of metabolic compounds in an ecosystem
chytridiomycosis disease of amphibians caused by the fungus Batrachochytrium dendrobatidis; thought to be a major cause of the global amphibian decline
DNA barcoding molecular genetic method for identifying a unique genetic sequence to associate with a species
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